Bag-pressing members for packaging machine

ABSTRACT

A machine for opening thin, flexible walled bags as the bags are advanced edgewise along a predetermined path in upright positions with the walls of each bag positioned face-to-face and with the upper end portions of the bags straddling a splitter bar. To force the walls of each bag apart, air is expelled through an orifice in the splitter bar and into the bag. In timed relation with the expelling of air into the bag, a pair of pressing members are moved into engagement with the upper end portions of the walls to press the walls against the splitter bar and prevent escape of the air. To move the pressing members into engagement with the bags, an air-operated actuator is mounted on the upper edge portion of the splitter bar and is connected to the pressing members.

United States Patent I 72] Inventor Robert F. Lense Rockford, Ill. [21]Appl. No. 852,356 [22] Filed Aug. 22, 1969 [4S] Patented July 13, 1971[73] Assignee Riegel Paper Corporation New York, N.Y.

[54] BAG-PRESSING MEMBERS FOR PACKAGING MACHINE 13 Claims, 5 DrawingFigs.

[52] US. Cl 53/385 [51] Int. Cl B65b 43/36 [50] Field ofSearch 53/385,386, 183, 187,124B

[56] Reierences Cited UNITED STATES PATENTS 2,885,846 5/1959 I-Iarker53/124 3,471,997 10/1969 Berry 53/386 3,260,170 7/1966 Barraclough53/385 X Primary ExaminerTheron E. Condon Assistant Examiner Horace M.Culver Attorney-Wolfe, Hubbard, Leydig, Voit & Osann ABSTRACT: A machinefor opening thin, flexible walled bags as the bags are advanced edgewisealong a predetermined path in upright positions with the walls of eachbag positioned faceto-face and with the upper end portions of the bagsstraddling a splitter bar. To force the walls of each bag apart, air isexpelled through an orifice in the splitter bar and into the bag. Intimed relation with the expelling of air into the bag, a pair ofpressing members are moved into engagement with the upper end portionsof the walls to press the walls against the splitter bar and preventescape of the air. To move the pressing members into engagement with thebags, an air-operated actuator is mounted on the upper edge portion ofthe splitter bar and is connected to the pressing members.

BAG-PRESSING MEMBERS FOR PACKAGING MACHINE BACKGROUND OF THE INVENTIONThis invention relates to a packaging machine for opening and fillingthin, flexible walled bags as the bags are advanced edgewise along apredetermined path in upright positions with the walls of each bagpositioned face-to-face. Before filling of the bags, gas is injectedinto each bag to force the walls apart and, in timed relation, amechanism moves pressing members against the upper edge portions of thewalls of the bag to force the upper edge portions toward one another toprevent escape of gas from the bag so that the walls of the bag will beforced apart by the gas.

SUMMARY OF THE INVENTION It is the primary object of the presentinvention to provide the machine with a unique mechanism for moving thepressing members such that there is more clearance around the bag path,less likelihood of the machine jamming due to malfunctions of themechanism, and more ease in changing the posi tion of the pressingmembers along the path than has been possible heretofore in machines ofa similar nature.

It is a more detailed object to accomplish the above by moving thepressing members with a fluid operated actuator,

mounted on a splitter bar which is positioned stationarily in the pathwith the upper end portions of the walls of each bag straddling the barand adapted to be pressed against the bar by the pressing members.

It is a further object of the present invention to provide a novelmounting arrangement for mounting both pressing members on a singlefluid-operated actuator for movement of the pressing members in unisonand, more specifically, the pressing members are mounted on the lowerend portions of arms which are pivotally connected intermediate theirends to the actuator with the actuator operable to swing the arms andmove the pressing members toward the splitter bar.

It is another object of the present invention to provide pressingmembers which have a longer life and engage the walls while conformingmore easily to any irregularities in the walls or the splitter bar thanpressing members previously used in similar machines.

Other objects and advantages of the invention will become apparent fromthe following detailed description when taken in connection with theaccompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is afragmentary perspective view schematically showing a machine embodyingthe novel features of the present invention.

FIG. 2 is an enlarged fragmentary elevational view of a portion of FIG.1 and showing the fluid-operated actuator and the pressing member on oneside of the path.

FIG. 3 is an end view of the actuator of FIG. 2 and showing the pressingmembers out of engagement with the walls of the bag.

FIG. 4 is a cross section taken substantially along the line 4-4 of FIG.2 and showing the pressing members engaging the walls of the bag.

FIG. 5 is a cross section taken substantially along the line 5-5 of FIG.2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in thedrawings for purposes of illustration, the invention is embodied in apackaging machine (FIG. 1) for opening and filling thin, flexible walledbags 11 as the bags are advanced edgewise and open end up along apredetermined path with the walls 12 (FIG. 4) positioned face-to-faceand with the upper end portions of the walls straddling a splitter bar13 (FIG. I) which is positioned stationarily in the path. The bags areformed from continuous strips of flexible material joined together atthe bottom by a fold 14 (FIG. 4) and sealed vertically by a sealer (notshown) to form side seals 15 (FIG. 2) at predetermined intervals alongthe strips. Downstream of the sealer, the strips are cut along thevertical centerline of the seals by a cutter 17 (FIG. 1) to separate theindividual bags which are then gripped and supported for furthermovement along the path by clamps 18 carried on a power-driven chain18a.

As each bag 11 advances along the path, the bag passes through anopening station in which suction cups l9 grip the walls 12 of the bagand pull the walls apart to open the bag widely so that the bag can befilled rapidly with a product which is introduced into the bag through aspout 20. The formation of the bags in the above manner creates anattraction between the inside faces of the walls of each bag, the attraction causing the bags to resist opening by the suction cups.

To open the bags 11 partially thus breaking the interface attraction andpreparing them for full opening by the suction cups 19, a gas, in thisinstance air, is blown into the bags to force the walls apart. Herein,the air is expelled periodically through a downwardly opening orifice 21(FIG. 4) formed in the splitter bar 13. An inlet pipe 22 communicatingwith the orifice is fixed to the side of the splitter blade and isconnected to an air pressure source (not shown). To prevent the air fromsimply escaping out the top of each bag instead of remaining in the bagand forcing the walls apart, two pressing members 23 (FIG. 3) positionedon opposite sides of the path are periodically moved by a mechanism 24into engagement with the upper end portions of the walls 12 in timedrelation with the blowing of air into the bag so as to force the upperend portions of the walls toward one another and into engagement withthe splitter bar thus closing the top of the bag sufficiently to preventthe escape of air.

In accordance with the present invention, the mechanism 24 for movingthe pressing members 23 periodically into and out of engagement with thewalls 12 of each bag 11 is a fluidoperated actuator which preferably isadjustably mounted on the upper edge portion of the splitter bar 13 withthe pressing members suspended from the actuator. With this arrangement,the actuator is more compact than mechanisms heretofore used, and thereis more clearance around the path, less chance of the machine 10 jammingdue to mechanical failure, and greater ease in adjusting the positionsof the pressing members than has been true of prior mechanisms formoving the pressing members.

For mounting the actuator 24 on the splitter bar 13, a pair of flanges25 (FIG. 4) depend from the bottom of the housing 26 of the actuator anddefine a longitudinally extending slot 27 therebetween. The actuator ispositioned on the splitter bar with the upper edge portion of thesplitter bar inserted into the slot and is held in position by a pair ofsetscrews 28 (FIG. 2) which extend through one of the flanges and bearagainst the splitter bar. when it is desired to change the position ofthe pressing members 23 along the path, the setscrews are loosened, andthe actuator and the pressing members can then be slid along thesplitter bar to a new location.

To mount each pressing member 23 for movement toward and away from thewalls 12 of the bags 11 and the splitter bar 13, the pressing member ismounted on the lower end portion of an arm 29 (F IG. 4) which ispivotally mounted intermediate its ends between a depending bifurcatedflange 30 (FIG. 2) on the housing 26 of the actuator 24, and a pin 31extends through the flange and through a bushing 32 (FIG. 4) in the arm.A cam follower 33 is journaled in the upper end portion of each arm toturn about a generally vertical axis. To move the pressing members onthe lower end portions of the arms inwardly toward the splitter bar, atapered cam 35 (FIG. 5) is moved longitudinally of the bag path andbetween the cam followers thus forcing the latter outwardly to swing theupper ends of the arms outwardly. As the cam forces the upper ends ofthe arms to swing outwardly, the arms pivot about the pins 31 and thelower ends of the arms swing inwardly. A contractile spring 36 (FIG. 4)is connected to and extends between the arms above the pins 31 thusbiasing the cam followers toward one another and against the cam. As thecam is moved from between the cam followers to allow the upper ends ofthe arm to swing toward one another under influence of the spring, thelower ends of the arms swing away from the splitter bar.

In this instance, the cam 35 is telescoped on the piston rod 37 (FIG. ofthe actuator 24. At one end (the right end in FIG. 5), the piston rod isconnected by a screw 38 to a piston 39 which is positioned within achamber 40 formed in the housing 26. To move the cam 35 to the left andmove the pressing members 23 into engagement with the walls 12 of onebag I 1, pressure fluid, herein air, is forced into the head end of thechamber through a port 42 thus forcing the piston and piston rod to theleft. The interior of the chamber is lined with a rubber diaphragm 43which is connected to the head end of the piston to maintain the chamberairtight as the piston moves. A spring 44 (FIG. 5) biases the piston andpiston rod to the right to return the cam to a position freeing theupper ends of the arms 29 for inward swinging. As shown most clearly inFIG. 5, the spring is telescoped over the piston rod and is biasedbetween a washer 45 on the piston rod and a cap 46 in the rod end of theactuator housing, the washer bearing against one end of the cam. The endof the piston rod opposite the piston is slidably telescoped in abushing 48 (FIG. 5) mounted in an axial bore 49 in the cap 46 and, toenable adjustment of the stroke of the piston and thus the action of thecam 35, a screw 50 extends through the end of the cap and into the boreto engage the end of the piston rod. The extent to which the screwextends into the bore determines the degree of travel of the piston rodand thus the piston to the left under the force of the air introducedinto the chamber 40. Thus, by adjusting the travel of the piston rod,the extent to which the cam forces the arms outwardly can be changed tovary the movement of the pressing members 23 toward the splitter bar 13.

With the above arrangement, the piston 39 and piston rod 37 with thetapered cam 35 are normally biased to the right and held by the spring44 in a position in which the cam does not force the cam followers 33outwardly thus allowing the pressing members 23 to be held in positionsaway from the splitter bar 13 by action of the spring 36 on the upperend portions of the arms 29. To move the piston at predeterminedintervals to swing the pressing members toward the splitter bar, airunder pressure is forced into the chamber 40 through the port 42. Theadmission of the air is controlled by a three-way valve 52 (FIG. 2) in aline 53 leading to the port. A cam 54 on the cycle shaft 54a of themachine controls the opening and closing of the valve. When the cam 54opens the valve, air is forced into the chamber, and the pressingmembers are moved into engagement with the walls 12 of one bag 11 andthe splitter bar 13. As the cam continues to revolve with the cycleshaft, the valve is vented to the atmosphere and disconnects the airsource from the chamber. The spring 44 thus forces the piston to theright with the air exhausting from the chamber through the port 42 andthe exhaust port of the valve. The timing of the above operation iscontrolled by the shape of the cam and is such that the pressing membersengage the bag walls when air is injected into the bag.

The lower end portion of each arm 29 is formed in two parts to allow forvertical adjustment in the location of the pressing members 23. Achannel-shaped link 55 (FIG. 4) forms the lower part of each arm and isconnected to the upper part of the arm by a screw 56. For verticaladjustability, the upper end portion of each link is formed with avertically extending slot 56a (FIG. 2) through which the screw 56extends. The link ,y ;,.can be moved vertically to the desired location,and then the screw can be tightened to hold the link in place. Toconnect each pressing member to its respective arm, a rod 57 (FIG. 4)extends from the back of the pressing member and through a hole 58formed in the lower end portion of the link. A slot 59 (FIG. 2) extendsdownwardly from the hole splitting the lower end portion of the linkinto two parts, and a screw 60 extends through the two parts. Theposition of the pressing member 23 laterally of the arm and the splitterbar 13 can be adjusted by sliding the rod through the hole to thedesired location and then turning the screw 60 to force the two parts ofthe lower end portion of the link toward one another to clamp the rod inthe link.

Advantageously, each pressing member 23 is formed by a roller 62 (FIG.4) journaled for rotation in a support 63 and surrounded by a cover 64of yieldably resilient material such as rubber formed as a tube andtelescoped over the roller. With this arrangement, the roller is free torotate thus exposing the entire surface of the cover to wear, thisarrangement resulting in a longer service life for the cover.Additionally, this arrangement allows the pressing members to conform toany irregularities in the surfaces of the bag walls 12 and the splitterbar 13. The support 63 is formed by an elongated rectangular back memberwhich is rigidly fixed to one end of the rod 57 and by a pair of sideflanges which extend out wardly at right angles on each end of the backmember. The roller 62 is journaled on and supported between the flangesby pins 66 (FIG. 2) and extends longitudinally of the splitter bar. Asshown in FIG. 2, the roller is longer than the edge-to-edge length ofthe bag 11 so as to engage the bag along its entire length.

It will be observed that providing the machine 10 with thefluid-operated actuator 24 to move the pressing members 23 and, moreparticularly, mounting the actuator above the bag path is a particularlyadvantageous arrangement. With this arrangement, there is greaterclearance around the bag path and the bag 11, and there is lesslikelihood of the machine jamming due to a malfunction than has beentrue of most previous devices wherein a series of linkages driven by themachine cycle shaft are connected to pressing members to move thelatter. Moreover, mounting the actuator on the upper edge portion of thesplitter bar 13 together with the elimination of mechanical linkagesfrom the pressing members to the cycle shaft 54a results in easieradjustment of the pressing members longitudinally along the path. Theutilization of the fluid-operated actuator allows the timing control forthe operation of the pressing members to be optionally located remotelyfrom the physical location of the pressing members rather than on thecycle shaft in the immediate vicinity of the pressing members asrequired by the mechanical linkages previously used. Further, theparticular construction of the actuator is particularly well adapted tooperate both pressing members and to operate the latter in unison.Another advantage is the formation of the pressing members as rollers 62with covers 64 of resiliently yieldable material, this arrangementresulting in a longer service life for the pressing members and moresure contact between the bag wall 12 and the splitter bar 13 even if thesurface of the splitter bar IS uneven.

I claim:

I. In a machine for opening thin, flexible walled bags as the bags areadvanced edgewise along a predetermined path in upright positions withthe walls of each bag positioned face-toface, the combination of,splitter bar positionable between the walls of each successive bag forperiodically injecting gas into the bag to force apart the walls,mechanism for pressing the upper edge portions of the walls toward oneanother to seal the bag around said splitter bar said mechanism beingmovable between positions in and out of engagement with the walls, and afluid-operated actuator adjustably and removably mounted on saidsplitter bar whereby the location of said actuator along said path maybe changed andsaid actuator may be easily removed for servicing, saidactuator having a reciprocating rod operably connected to saidmechanism, and being operable to reciprocate said rod and thereby movesaid mechanism into pressing engagement with the walls in timed relationwith the injecting of gas into the bag to prevent escape of gas from thebag so that the walls of the bag are forced apart.

2. The machine of claim I in which said splitter bar is disposed betweenthe upper end portions of the walls to hold the latter apart and inwhich said actuator is mounted on said splitter bar above the path.

3. The machine of claim 1 in which the splitter bar is disposed betweenthe upper end portions of the walls to hold the latter apart, saidmechanism including a pair of arms with one arm positioned on each sideof the path, a pressing member mounted on each arm, and said actuatorbeing operably connected to said arms to move the pressing members intoengagement with the upper end portions of the walls to press said upperend portions against said splitter bar to prevent the escape of gas.

4. The machine of claim 3 in which said pressing members compriserollers which extend longitudinally of the path and which are at leastas long as the edgewise length of one bag so that said pressing membersengage the upper end portions of the walls along the entire length ofthe walls.

5. The machine of claim 4 in which said rollers are covered with aresiliently yieldable material whereby the rollers may conform to anyirregularities in the surface of the splitter bar and still press thewalls against the splitter bar sufficiently to prevent the escape ofgas.

6. The machine of claim 5 in which said rollers are journaled in saidarms to turn about axes extending longitudinally of said path wherebythe entire surface of each roller may be used to engage the walls toreduce wear of the rollers.

7. The machine of claim 3 in which each said arm is pivotally connectedintermediate its ends to said actuator to turn about an axis extendingparallel to the path, each said pressing member being connected to oneof said arms on one end portion of that arm, and said actuator beingoperable to engage each arm on the other end portion to force said otherend portion outwardly away from the path whereby the arm swings aboutthe pivotal connection thus moving the pressing member toward the path.

8. The machine of claim 7 in which the actuator is mounted on thesplitter bar above the path.

9. The machine of claim 8 in which the pressing members are mounted onsaid arms for adjustment laterally of said path.

10. In a machine for opening thin, flexible walled bags as the bags areadvanced edgewise along a predetermined path in upright positions withthe walls of each bag positioned face-toface, the combination of, asplitter bar positioned stationary along said path with each bag passingalong the splitter bar with the upper end portions of the wallsstraddling the bar, said bar having an orifice opening downwardly at thelower edge of the bar, means for periodically expelling gas through saidorifice and into each successive bag to force apart the walls, means forpressing the upper end portions of the walls against the splitter baradjacent said orifice, said pressing means being movable betweenpositions in and out of engagement with the walls, a fluid-operatedactuator positioned above the path with said pressing means suspendedfrom said actuator, said actuator being adjustably mounted on saidsplitter bar so that the actuator and said pressing means can be movedto a plurality of positions longitudinally of the path, and saidactuator having a reciprocating rod operable to move said pressing meansinto pressing engagement with the walls in timed relation with theexpelling of gas into the bag to prevent escape of the gas from the bagso that the walls of the bag are forced apart.

11. The machine of claim 10 in which said pressing means comprise twoarms pivotally connected intermediate their ends to opposite sides ofsaid actuator to swing toward and away from the path, a cylindricalmember mounted on the lower end portion of each arm and extendinglongitudinally of the path with each cylindrical member being longerthan the edge-to-edge length of one bag, and means on said actuator toswing said arms in unison to force the cylindrical members against theupper edge portions of the walls.

12. The machine of claim 11 in which said cylindrical members arerotatably mounted on said arms so that each said member may be turned toreduce the wear on any given part of the member and increase the usablelife of the member.

13. In a machine for opening thin, flexible walled bags as the bags areadvanced along a predetermined path in upri ht positions with the wallsof each bag positioned face-toace, the

combination of, a splitter bar positioned stationarily along said pathwith each bag passing along the splitter bar with the upper end portionsof the walls straddling the bar, said bar having an orifice openingdownwardly at the lower edge of the bar, means for periodicallyexpelling gas through said orifice and into each successive bag to forceapart the walls, a fluidoperated actuator having a housing adjustablymounted on the splitter bar, a pair of arms pivotally connectedintermediate their ends to said housing on opposite sides of the path, aroller rotatably mounted on the lower end portion of each arm, a pistonrod mounted in said housing for sliding movement longitudinally of thepath, a cam telescoped on said piston rod with the upper end portions ofthe arms positioned to engage opposite sides of said cam as the pistonrod slides, said cam being tapered outwardly away from the path at theopposite sides, and means for sliding said piston rod in timed relationwith the expelling of gas into the bag, whereby as the piston rod slidesin one direction, the cam forces the upper end portions of the armsoutwardly away from the path to swing the lower end portions of the armstoward the path and thus move the rollers into engagement with the upperend portions of the walls to press the upper end portions of the wallsagainst the splitter bar and prevent escape of gas from the bag so thatthe walls of the bag may be forced apart.

1. In a machine for opening thin, flexible walled bags as the bags areadvanced edgewise along a predetermined path in upright positions withthe walls of each bag positioned face-to-face, the combination of,splitter bar positionable between the walls of each successive bag forperiodically injecting gas into the bag to force apart the walls,mechanism for pressing the upper edge portions of the walls toward oneanother to seal the bag around said splitter bar said mechanism beingmovable between positions in and out of engagement with the walls, and afluid-operated actuator adjustably and removably mounted on saidsplitter bar whereby the location of said actuator along said path maybe changed and said actuator may be easily removed for servicing, saidactuator having a reciprocating rod operably connected to saidmechanism, and being operable to reciprocate said rod and thereby movesaid mechanism into pressing engagement with the walls in timed relationwith the injecting of gas into the bag to prevent escape of gas from thebag so that the walls of the bag are forced apart.
 2. The machine ofclaim 1 in which said splitter bar is disposed between the upper endportions of the walls to hold the latter apart and in which saidactuator is mounted on said splitter bar above the path.
 3. The machineof claim 1 in which the splitter bar is disposed between the upper endportions of the walls to hold the latter apart, said mechanism includinga pair of arms with one arm positioned on each side of the path, apressing member mounted on each arm, and said actuator being operablyconnected to said arms to move the pressing members into engagement withthe upper end portions of the walls to press said upper end portionsagainst said splitter bar to prevent the escape of gas.
 4. The machineof claim 3 in which said pressing members comprise rollers which extendlongitudinally of the path and which are at least as long as theedgewise length of one bag so that said pressing members engage theupper end portions of the walls along the entire length of the walls. 5.The machine of claim 4 in which said rollers are covered with aresiliently yieldable material whereby the rollers may conform to anyirregularities in the surface of the splitter bar and still press thewalls against the splitter bar sufficiently to prevent the escape ofgas.
 6. The machine of claim 5 in which said rollers are journaled insaid arms to turn about axes extending longitudinally of said pathwhereby the entire surface of each roller may be used to engage thewalls to reduce wear of the rollers.
 7. The machine of claim 3 in whicheach said arm is pivotally connected intermediate its ends to saidactuator to turn about an axis extending parallel to the path, each saidpressing member being connected to one of said arms on one end portionof that arm, and said actuator being operable to engage each arm on theother end portion to force said other end portion outwardly away fromthe path whereby the arm swings about the pivotal connection thus movingthe pressing member toward the path.
 8. The machine of claim 7 in whichthe actuator is mounted on the splitter bar above the path.
 9. Themachine of claim 8 in which the pressing members are mounted on saidarms for adjustment laterally of said path.
 10. In a machine for openingthin, flexibLe walled bags as the bags are advanced edgewise along apredetermined path in upright positions with the walls of each bagpositioned face-to-face, the combination of, a splitter bar positionedstationary along said path with each bag passing along the splitter barwith the upper end portions of the walls straddling the bar, said barhaving an orifice opening downwardly at the lower edge of the bar, meansfor periodically expelling gas through said orifice and into eachsuccessive bag to force apart the walls, means for pressing the upperend portions of the walls against the splitter bar adjacent saidorifice, said pressing means being movable between positions in and outof engagement with the walls, a fluid-operated actuator positioned abovethe path with said pressing means suspended from said actuator, saidactuator being adjustably mounted on said splitter bar so that theactuator and said pressing means can be moved to a plurality ofpositions longitudinally of the path, and said actuator having areciprocating rod operable to move said pressing means into pressingengagement with the walls in timed relation with the expelling of gasinto the bag to prevent escape of the gas from the bag so that the wallsof the bag are forced apart.
 11. The machine of claim 10 in which saidpressing means comprise two arms pivotally connected intermediate theirends to opposite sides of said actuator to swing toward and away fromthe path, a cylindrical member mounted on the lower end portion of eacharm and extending longitudinally of the path with each cylindricalmember being longer than the edge-to-edge length of one bag, and meanson said actuator to swing said arms in unison to force the cylindricalmembers against the upper edge portions of the walls.
 12. The machine ofclaim 11 in which said cylindrical members are rotatably mounted on saidarms so that each said member may be turned to reduce the wear on anygiven part of the member and increase the usable life of the member. 13.In a machine for opening thin, flexible walled bags as the bags areadvanced along a predetermined path in upright positions with the wallsof each bag positioned face-to-face, the combination of, a splitter barpositioned stationarily along said path with each bag passing along thesplitter bar with the upper end portions of the walls straddling thebar, said bar having an orifice opening downwardly at the lower edge ofthe bar, means for periodically expelling gas through said orifice andinto each successive bag to force apart the walls, a fluid-operatedactuator having a housing adjustably mounted on the splitter bar, a pairof arms pivotally connected intermediate their ends to said housing onopposite sides of the path, a roller rotatably mounted on the lower endportion of each arm, a piston rod mounted in said housing for slidingmovement longitudinally of the path, a cam telescoped on said piston rodwith the upper end portions of the arms positioned to engage oppositesides of said cam as the piston rod slides, said cam being taperedoutwardly away from the path at the opposite sides, and means forsliding said piston rod in timed relation with the expelling of gas intothe bag, whereby as the piston rod slides in one direction, the camforces the upper end portions of the arms outwardly away from the pathto swing the lower end portions of the arms toward the path and thusmove the rollers into engagement with the upper end portions of thewalls to press the upper end portions of the walls against the splitterbar and prevent escape of gas from the bag so that the walls of the bagmay be forced apart.